Methods of fabricating a composite carbon nanotube thermal interface device

ABSTRACT

Embodiments of a composite carbon nanotube structure comprising a number of carbon nanotubes disposed in a matrix comprised of a metal or a metal oxide. The composite carbon nanotube structures may be used as a thermal interface device in a packaged integrated circuit device.

RELATED APPLICATION

[0001] This application is related to application Ser. No.______ ,entitled “Method of Fabricating a Composite Carbon Nanotube ThermalInterface Device”, filed on even date herewith.

FIELD OF THE INVENTION

[0002] The invention relates generally to the packaging of an integratedcircuit die and, more particularly, to methods for manufacturing acomposite carbon nanotube structure that may be used as a thermalinterface device.

BACKGROUND OF THE INVENTION

[0003] Illustrated in FIG. 1 is a conventional packaged integratedcircuit device 100. The integrated circuit (IC) device 100 may, forexample, comprise a microprocessor, a network processor, or otherprocessing device, and the IC device 100 may be constructed usingflip-chip mounting and Controlled Collapse Chip Connection (or “C4”)assembly techniques. The IC device 100 includes a die 110 that isdisposed on a substrate 120, this substrate often referred to as the“package substrate.” A plurality of bond pads on the die 110 areelectrically connected to a corresponding plurality of leads, or“lands”, on the substrate 120 by an array of connection elements 130(e.g., solder balls, columns, etc.). Circuitry on the package substrate120, in turn, routes the die leads to locations on the substrate 120where electrical connections can be established with a next-levelcomponent (e.g., a motherboard, a computer system, a circuit board,another IC device, etc.). For example, the substrate circuitry may routeall signal lines to a pin-grid array 125—or, alternatively, a ball-gridarray—formed on a lower surface of the package substrate 120. Thepin-grid (or ball-grid) array then electrically couples the die to thenext-level component, which includes a mating array of terminals (e.g.,pin sockets, bond pads, etc.).

[0004] During operation of the IC device 100, heat generated by the die110 can damage the die if this heat is not transferred away from the dieor otherwise dissipated. To remove heat from the die 110, the die isultimately coupled with a heat sink 170 via a number of thermallyconductive components, including a first thermal interface 140, a heatspreader 150, and a second thermal interface 160. The first thermalinterface 140 is coupled with an upper surface of the die 110, and thisthermal interface conducts heat from the die and to the heat spreader150. Heat spreader 150 conducts heat laterally within itself to “spread”the heat laterally outwards from the die 110, and the heat spreader 150also conducts the heat to the second thermal interface 160. The secondthermal interface 160 conducts the heat to heat sink 170, whichtransfers the heat to the ambient environment. Heat sink 170 may includea plurality of fins 172, or other similar features providing increasedsurface area, to facilitate convection of heat to the surrounding air.The IC device 100 may also include a seal element 180 to seal the die110 from the operating environment.

[0005] The efficient removal of heat from the die 110 depends on theperformance of the first and second thermal interfaces 140, 160, as wellas the heat spreader 150. As the power dissipation of processing devicesincreases with each design generation, the thermal performance of thesedevices becomes even more critical. To efficiently conduct heat awayfrom the die 110 and toward the heat sink 170, the first and secondthermal interfaces 140, 160 should efficiently conduct heat in atransverse direction (see arrow 105).

[0006] At the first thermal interface, it is known to use a layer ofthermal grease disposed between the die 110 and the heat spreader 150.Thermal greases are, however, unsuitable for high power—and, hence, highheat—applications, as these materials lack sufficient thermalconductivity to efficiently remove a substantial heat load. It is alsoknown to use a layer of a low melting point metal alloy (e.g., a solder)as the first thermal interface 140. However, these low melting pointalloys are difficult to apply in a thin, uniform layer on the die 110,and these materials may also exhibit low reliability. Examples ofmaterials used at the second thermal interface include thermallyconductive epoxies and other thermally conductive polymer materials.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]FIG. 1 is a cross-sectional elevation view of a conventionalintegrated circuit package.

[0008]FIG. 2 is a block diagram illustrating one embodiment of a methodof fabricating a composite carbon nanotube structure.

[0009]FIGS. 3A-3G are schematic diagrams illustrating an embodiment ofthe method for fabricating a composite carbon nanotube structure, asshown in FIG. 2.

[0010]FIGS. 4A-4B are schematic diagrams illustrating furtherembodiments of the method for fabricating a composite carbon nanotubestructure, as shown in FIG. 2.

[0011]FIG. 5 is a block diagram illustrating a second embodiment of amethod of fabricating a composite carbon nanotube structure.

[0012]FIGS. 6A-6F are schematic diagrams illustrating an embodiment ofthe method for fabricating a composite carbon nanotube structure, asshown in FIG. 5.

[0013]FIG. 7 is a schematic diagram of a computer system including anintegrated circuit device having a composite carbon nanotube structureconstructed according to the method of FIG. 2 or the method of FIG. 5.

[0014]FIG. 8 is a perspective view of an example of a conventionalcarbon nanotube.

DETAILED DESCRIPTION OF THE INVENTION

[0015] Illustrated in FIGS. 2 through 6F are embodiments of methods forfabricating a composite carbon nanotube structure that may be used as athermal interface device in an IC device (e.g., the IC device 100 ofFIG. 1). In one of the disclosed embodiments, a number of carbonnanotubes are formed in a porous metal oxide layer that has beendeposited on a sacrificial substrate. In a second disclosed embodiment,a composite carbon nanotube structure is grown on a substrate using aplating process, wherein carbon nanotubes are dispersed in the platingbath. The disclosed embodiments are explained below in the context ofmanufacturing thermal interface devices for IC chips; however, it shouldbe understood that the disclosed thermal interface devices and themethods for their production may find application in a wide variety ofapplications where a thermally conductive element is needed or where acomposite carbon nanotubes structure is desired (e.g., field emissiondisplays, data storage devices, as well as other electronic and photonicdevices).

[0016] An example of a typical carbon nanotube 800 is shown in FIG. 8.The carbon nanotube (or “CNT”) is generally cylindrical in shape and maybe single walled or multi-walled. The carbon nanotube 800 extends alonga primary axis 805, and the nanotube 800 has a height 810 and a diameter820. The height 810 may be up to 50 μm in length for a multi-walledcarbon nanotube and up to 2 cm in length for a single walled carbonnanotube. For multi-walled carbon nanotubes, the diameter 820 may be upto 100 nm, and for single walled carbon nanotubes, the diameter 820 maybe up to 30 nm. Carbon nanotubes are characterized by high mechanicalstrength, good chemical stability, and high thermal conductivity,especially in a direction along their primary axis 805.

[0017] Illustrated in FIG. 2 is an embodiment of a method 200 offabricating a composite carbon nanotube structure comprising an array ofcarbon nanotubes disposed within a porous metal oxide matrix. Also, themethod 200 of FIG. 2 is further illustrated in FIGS. 3A through 3G, aswell as FIGS. 4A-4B, and reference should be made to these figures alongwith FIG. 2, as called out in the text.

[0018] Referring now to block 210 in FIG. 2, a sacrificial layer isformed on a substrate. This is illustrated in FIG. 3A, where asacrificial layer 320 has been formed on a substrate 310. Thesacrificial layer 320 may comprise any suitable material that will allowfor separation of the final composite structure from the substrate 310,as will be described in greater detail below. Materials suitable for thesacrificial layer include, by way of example, Vanadium (V), Titanium(Ti), Tungsten (W), and alloys thereof. The sacrificial layer 320 may bedeposited using any suitable deposition technique, including chemicalvapor deposition (CVD), physical vapor deposition (PVD) techniques suchas sputtering, as well as electroplating and electroless plating.

[0019] The substrate 310 may comprise any suitable material upon which acomposite carbon nanotube structure can be constructed, such as, forexample, a silicon or a ceramic material. As noted above, in oneembodiment, the composite carbon nanotube structure to be fabricated onthe substrate 310 will ultimately be separated from the substrate.However, in other embodiments, the composite carbon nanotube structureis formed directly on a component, such as an integrated circuit die, asemiconductor wafer, a heat spreader, or a heat sink.

[0020] As set forth at block 220, a metal layer is deposited on thesacrificial layer. This is illustrated in FIG. 3B, where a metal layer330 has been formed on the sacrificial layer 320. In one embodiment, themetal layer 330 comprises Aluminum (Al). However, the metal layer 320may comprise other suitable metals, including Nickel (Ni) or Silicon(Si). The metal layer 330 may be formed using any suitable depositiontechnique, including CVD, electroplating, electroless plating, orsputtering.

[0021] Referring to block 230, the metal layer is anodized to form aporous metal oxide layer. This is shown in FIG. 3C, where the metallayer 330 has been anodized to form a porous metal oxide layer 340, andthis metal oxide layer 340 includes a number of pores 342. In oneembodiment, where the metal layer 330 comprises Aluminum, the metaloxide layer 340 comprises Aluminum Oxide (Al₂O₃). However, it should beunderstood that the metal oxide layer 340 may comprise an oxide of othermetals (e.g., Nickel Oxide, Silicon Oxide). Any suitable anodizationprocess may be employed to anodize the metal layer 330. In oneembodiment, the metal layer 330 is anodized in the presence of an acid(e.g., phosphoric acid, succinic acid, sulfuric acid, or oxalic acid)under a positive voltage in a range of between 1 and 60 volts. ForAluminum, as well as other metals, porosity in a range of betweenapproximately 30% and 70% (by volume) can be achieved.

[0022] In FIG. 3C, for ease of illustration, the metal layer 330 isrepresented as being fully anodized to a porous metal oxide layer 340.However, it should be understood that, in practice, only portions of themetal layer 330 may be anodized to form a metal oxide. This isillustrated in FIG. 4A, where portions of the metal layer 330 have beenanodized to form metal oxide layer 340 including pores 342, whereasother portions of the metal layer 330 remain unanodized. As shown inFIG. 4A, at least a portion of the metal layer surrounding each pore 342has been anodized to form a metal oxide 340, and this layer of metaloxide surrounding the pores may be referred to as the “barrier layer.”

[0023] With reference still to FIG. 4A, it can be seen that the bottomends 344 of the pores 340 (or at least some of the pores) do not extendto the sacrificial layer 320. As will be described below, carbonnanotubes will be grown in the pores 342 of metal oxide layer 340 and,upon separation from the sacrificial layer 320 and substrate 310, carbonnanotubes grown in the pores 342 would not extend through the metaloxide layer 340 (i.e., their ends will be covered by a thin layer 349 ofthe metal oxide barrier layer). This thin layer of metal oxide remainingon the carbon nanotubes may affect the thermal performance of theresulting composite carbon nanotube structure. Accordingly, as shown atblock 240, excess material may be removed from the pores 342 of themetal oxide layer 340. This is illustrated in FIGS. 3D and 4B, where thethin layer 349 of metal oxide has been removed from the lower ends ofthe pores 340, and the lower ends 346 of the pores 340 (see FIG. 4B) nowextend into the sacrificial layer 320 (or at least to the sacrificiallayer). Any suitable etching or other material removal process may beemployed to remove excess material from the pores.

[0024] Returning now to FIG. 2, and block 250 in particular, a catalystis selectively deposited within the pores 342 of the metal oxide layer340. This is illustrated in FIG. 4B, where catalyst 350 has beendeposited within the pores 342. Note that, as shown in FIG. 4B, thecatalyst 350 has been selectively deposited on the exposed portion ofthe sacrificial layer 320 at the bottom 346 of the pore 340. Thecatalyst 350 comprises any material upon which growth of a carbonnanotube can be initiated—i.e., the catalyst provides nucleation sites.Suitable catalysts include Iron (Fe), Nickel (Ni), Cobalt (Co), Rhodium(Rh), Platinum (Pt), Yttrium (Yt), and their combinations.

[0025] The selective deposition of the catalyst 350 may be achievedusing either an electroplating process or an electroless platingprocess. In an electroplating process, no plating occurs on the exposedmetal oxide surfaces within the pores 342 because sufficient electriccurrent will not pass through the dielectric metal oxide. In anelectroless plating process, the metal oxide material is not a catalyticmaterial for the plating process, and the catalyst 350 does not build upon exposed metal oxide surfaces. For an electroplating process, thesacrificial layer 320 is comprised of an electrically conductivematerial and, for an electroless plating process, the sacrificial layer320 is comprised of a suitable catalytic material (for the catalyst350).

[0026] Referring now to block 260, carbon nanotubes are formed in thepores of the metal oxide layer. This is illustrated in FIG. 3E, wherecarbon nanotubes 360 have been formed in the pores 342 of metal oxidelayer 340. The carbon nanotubes will be selectively (or at leastpreferentially) grown on the catalyst 350 within the pores 342 of metaloxide layer 340, and the carbon nanotubes will align themselves with thepores. Any suitable process may be employed to form the carbon nanotubes360, including CVD and plasma enhanced CVD (PECVD). Any suitabletechnique may be used to introduce carbon into the deposition chamber,including introducing a carbon-containing precursor (e.g., methane,ethylene, or acetylene), laser vaporization of carbon, electricaldischarge between carbon electrodes, or gas phase CVD using carbon andmetal carbonyls. The metal oxide layer 340 (and substrate 310) may alsobe heated during deposition (e.g., to a temperature of approximately800° C.).

[0027] In one embodiment, as shown in FIG. 3E, the carbon nanotubes 360may be grown to a height that extends above the upper surface of themetal oxide layer 340. The height of the carbon nanotubes 360 and theextent to which they extend above the upper surface of metal oxide layer340 is generally a function of the deposition time. Extending the carbonnanotubes 360 above the metal oxide layer 340 may improve the thermalconductivity of the resulting composite carbon nanotube structure byproviding improved contact between the carbon nanotubes 360 and anycomponent (e.g., a die, heat spreader, or heat sink) to which they arecoupled. In an alternative embodiment, rather than growing the carbonnanotubes 360 to a height above the metal oxide layer 340, an etchingprocess is performed to remove some of the metal oxide material, therebyexposing the ends of the carbon nanotubes.

[0028] In the embodiments described above, carbon nanotubes 360 aregrown within the pores 342 of a porous metal oxide layer 340. Metaloxides, such as Aluminum Oxide and oxides of other metals, are desirablebecause they can provide a regular and controlled pore structure.However, it should be understood that the disclosed embodiments are notlimited to growth of carbon nanotubes in metal oxide materials. Infurther embodiments, carbon nanotubes may be grown in other poroussubstances (e.g., a porous polymer material).

[0029] As set forth at block 270, the metal oxide matrix with carbonnanotubes is separated from the substrate to form a free-standingcomposite carbon nanotube structure. This is shown in FIG. 3F, where themetal oxide layer 340 including carbon nanotubes 360 has been separatedfrom the substrate 310 (and sacrificial layer 320) to form afree-standing composite carbon nanotube structure 300. In oneembodiment, this separation is accomplished by dissolution of thesacrificial layer 320. The sacrificial layer 320 may be dissolved in asolution containing an acid (e.g., phosphoric acid, succinic acid, orsulfuric acid). Alternatively, the sacrificial layer 320 may bedissolved in an acid-containing solution in the presence of an anodicpotential. The thickness of such a free-standing composite CNT structure300 may, in one embodiment, be in a range of approximately 2 μm to 20μm.

[0030] In a further embodiment, as set forth at block 280 in FIG. 2, thefree-standing composite carbon nanotube structure is attached to anothercomponent (e.g., a die, a heat spreader, a heat sink, etc.). This isillustrated in FIG. 3G, which shows a packaged IC device 301. Thepackaged IC device 301 includes a first thermal interface device 300 adisposed between an integrated circuit die 110 and a heat spreader 150.The IC package 301 may also include another thermal interface device 300b disposed between the heat spreader 150 and a heat sink 170. Each ofthe thermal interface devices 300 a, 300 b comprises a free-standingcomposite CNT structure, as shown in FIG. 3F. Any suitable technique maybe used to attach the composite CNT structure 300 a (or 300 b) to thedie 110 and heat spreader 150 (or heat spreader 150 and heat sink 170).In one embodiment, a low melting point metal alloy (e.g., solder) isused to couple the composite CNT structure 300 a (or 300 b) with each ofthe die 110 and heat spreader 150 (or heat spreader 150 and heat sink170), and the composite CNT structure may be mechanically pressedbetween these components (under, for example, a pressure in a range upto approximately 10 Kg/cm²) to insure sufficient thermal contact isachieved.

[0031] Illustrated in FIG. 5 is a second embodiment of a method 500 offabricating a composite carbon nanotube structure. Also, the method 500of FIG. 5 is further illustrated in FIGS. 6A through 6F, and referenceshould be made to these figures along with FIG. 5, as called out in thetext.

[0032] Referring now to block 510 in FIG. 5, carbon nanotubes aredispersed within a plating solution. This is illustrated in FIG. 6A,where a plating bath 605 includes a plating solution 680 to which carbonnanotubes 690 have been added. In one embodiment, the plating solution680 is adapted for electroplating, and in another embodiment, theplating solution 680 is adapted for electroless plating. The carbonnanotubes 690 may, in one embodiment, comprise up to approximately 20percent by weight of the plating solution 680. Also, the solution 680may be agitated to promote uniform dispersion of the carbon nanotubes690.

[0033] Note that, in FIG. 6A, a substrate 610 has been disposed withinthe plating bath 605. In one embodiment, the substrate 610 comprises anintegrated circuit die. In another embodiment, the substrate 610comprises a semiconductor wafer upon which integrated circuitry has beenformed (that is to be cut into a number of IC die). In a furtherembodiment, the substrate 610 comprises a heat spreader (e.g., the heatspreader 150 shown in FIG. 1), and in yet another embodiment, thesubstrate comprises a heat sink (e.g., the heat sink 170 of FIG. 1). Inyet a further embodiment, the substrate 610 comprises a sacrificialsubstrate that is ultimately separated from the structure formedthereon, as will be explained in more detail below.

[0034] For electroplating, the plating solution 680 comprises metal ions(of the metal to be plated on substrate 610) and an electrolyte, such assulfuric acid (H₂SO₄) or a base such as KOH (potassium hydroxide) orTMAH (tetramethylammonium hydroxide). The metal to be plated maycomprise, by way of example, Tin (Sn), Indium (In), Copper (Cu), Nickel(Ni), Cobalt (Co), Iron (Fe), Cadmium (Cd), Chromium (Cr), Ruthenium(Ru), Rhodium (Rh), Rhenium (Re), Antimony (Sb), Bismuth (Bi), Platinum(Pt), Gold (Au), Silver (Ag), Zinc (Zn), Palladium (Pd), Manganese (Mn),or alloys thereof. In another embodiment, the plating solution 680further comprises a complexing agent to complex ions in the platingsolution in order to change their solubility and oxidation/reductionpotential. For example, for Cobalt metal ions, citric acid can be usedas the complexing agent to make the Cobalt ions soluble in a basic (highpH) solution. In a further embodiment, the plating solution 680 alsoincludes one or more additives to regulate the material properties ofthe plated metal (e.g., polyethylene glycol or di-sulfides to regulategrain size).

[0035] For electroless plating, the plating solution comprises metalions (again, of the metal to be plated on substrate 610), one or morecomplexing agents, and one or more reducing agents. As set forthpreviously, the metal to be plated may comprise Tin, Indium, Copper,Nickel, Cobalt, Iron, Cadmium, Chromium, Ruthenium, Rhodium, Rhenium,Antimony, Bismuth, Platinum, Gold, Silver, Zinc, Palladium, Manganese,or alloys thereof. Also as noted above, a complexing agent comprises asubstance to complex ions in the plating solution in order to changetheir solubility and oxidation/reduction potential (see example above).The reducing agent (or agents) comprises any substance that will supplyelectrons to the plating bath 680 during the plating process, includingformaldehyde, hypophosphite, dimethyl amine borane, or hydrazinehydrate. In another embodiment, the plating solution 680 also includes asubstance to adjust the pH of the plating solution. In a furtherembodiment, the plating solution also includes one or more additives toregulate the properties of the deposited metal, as described above.

[0036] Referring next to block 520, a layer of metal is plated on thesubstrate, wherein this metal layer includes carbon nanotubes from theplating bath. This is illustrated in FIG. 6B, where a metal layer 620has been formed on the substrate 610, and this metal layer 620 includesa number of carbon nanotubes 690. Thus, a metal matrix 620 having carbonnanotubes 690 dispersed therein is formed on the substrate 610. Thecarbon nanotubes 690 in metal layer 620 originate from the platingsolution 680, and they are deposited on the substrate 610 along with themetal layer 620 during the plating process. Note that, in FIG. 6B (andFIG. 6C), the carbon nanotubes 690 are not shown in the plating solution680 (although present in this solution), which has been done simply forclarity and ease of illustration.

[0037] The metal layer 620 may be deposited on the substrate using anelectroplating process or an electroless plating process. Forelectroplating, in one embodiment, a seed layer may first be depositedon the substrate 610 prior to deposition of the metal layer 620. This isshown in FIG. 6C, where a seed layer 622 has been formed on thesubstrate 610. The seed layer 622 will typically comprise the same metalthat is to be plated on the substrate 610 (although the seed layer maybe a different metal), and this seed layer 622 may be deposited usingany suitable process (e.g., CVD). For electroless plating, a layer ofcatalyst 624 (also shown in FIG. 6C) may, in one embodiment, bedeposited on the substrate 610 prior to plating. The catalyst layer maycomprise a noble metal—e.g., Gold (Au), Palladium (Pd), Platinum (Pt),Ruthenium (Ru), Rhodium (Rh), Silver (Ag), Osmium (Os), or Iridium(Ir)—or a transition metal—e.g., Nickel (Ni), Cobalt (Co), or Iron(Fe)—or their alloys, and this layer may be deposited using any suitableprocess (e.g., CVD). Also, for electroplating, the plating solution 680is typically maintained at room temperature, whereas for electrolessplating, the plating solution 680 in plating bath 605 may be heated.

[0038] In one alternative embodiment, as set forth at block 530 in FIG.5, an electric field is applied across the substrate during formation ofthe metal layer. This is illustrated in FIG. 6D, where an electric field(E) 650 is applied across the substrate 610. Any suitable device may beemployed to apply the electric field 650 across the substrate 610. Forexample, the substrate 610 may be disposed between two plates, wherein avoltage is applied between the two plates to create an electric field(similar to a parallel plate capacitor). In the presence of an electricfield, a carbon nanotube will align itself with the electric field—i.e.,the primary axis 705 (see FIG. 7) of the carbon nanotubes will align inthe direction of the electric field 650 (see arrow 652)—and thisalignment will be maintained during the plating process. In oneembodiment, an electric field having a strength of approximately 10,000V/cm is applied to align the carbon nanotubes; however, it should beunderstood that an electric field of any suitable strength may beapplied, so long as the field induces the desired degree of alignment.As noted above, carbon nanotubes are excellent thermal conductors alongtheir primary axis, and alignment of the carbon nanotubes 690 in adirection parallel (or at least substantially parallel) with theelectric filed 650 will produce a metal matrix with carbon nanotubesthat has a high thermal conductivity in the direction of alignment(again, see arrow 652).

[0039] In another embodiment, where the substrate 610 comprises asacrificial substrate, the metal matrix layer 620 with carbon nanotubes690 is separated from the substrate, as denoted at block 540. This isshown in FIG. 6E, where the metal matrix layer 620 with carbon nanotubes690 has been separated from the substrate 610 to form a free-standingcomposite carbon nanotube structure 600. In one embodiment, thethickness of this free-standing composite CNT structure 600 may be in arange of 2 μm to 20 μm.

[0040] In a further embodiment, the free-standing composite carbonnanotube structure 600 is attached to another component (e.g., a die, aheat spreader, a heat sink, etc.). This is illustrated in FIG. 6F, whichshows a packaged IC device 601. The packaged IC device 601 includes afirst thermal interface device 600 a disposed between an integratedcircuit die 110 and a heat spreader 150. The IC package 601 may alsoinclude another thermal interface device 600 b disposed between the heatspreader 150 and a heat sink 170. Each of the thermal interface devices600 a, 600 b comprises a free-standing composite CNT structure, as shownin FIG. 6E. Any suitable technique may be used to attach the compositeCNT structure 600 a (or 600 b) to the die 110 and heat spreader 150 (orheat spreader 150 and heat sink 170). In one embodiment, a low meltingpoint metal alloy (e.g., solder) is deposited on a surface (or surfaces)of the composite CNT structure—see block 560 in FIG. 5—and this layer oflow melting point alloy is used to couple the composite CNT structure600 a (or 600 b) with the die 110 and/or heat spreader 150 (or heatspreader 150 and/or heat sink 170). In another embodiment, the platedmetal 620 itself comprises a low melting point metal or alloy, andattachment to the die 110 and/or heat spreader 150 (or heat spreader 150and/or heat sink 170) is accomplished by re-melting the metal matrixlayer 620.

[0041] An IC device having a thermal interface comprising afree-standing composite CNT structure—e.g., the packaged IC device 301of FIG. 3G having thermal interface devices 300 a, 300 b, or thepackaged IC device 601 of FIG. 6F having thermal interface devices 600a, 600 b—may find application in any type of computing system or device.An embodiment of such a computer system is illustrated in FIG. 7.

[0042] Referring to FIG. 7, the computer system 700 includes a bus 705to which various components are coupled. Bus 705 is intended torepresent a collection of one or more buses—e.g., a system bus, aPeripheral Component Interface (PCI) bus, a Small Computer SystemInterface (SCSI) bus, etc.—that interconnect the components of computersystem 700. Representation of these buses as a single bus 705 isprovided for ease of understanding, and it should be understood that thecomputer system 700 is not so limited. Those of ordinary skill in theart will appreciate that the computer system 700 may have any suitablebus architecture and may include any number and combination of buses.

[0043] Coupled with bus 705 is a processing device (or devices) 710. Theprocessing device 710 may comprise any suitable processing device orsystem, including a microprocessor, a network processor, an applicationspecific integrated circuit (ASIC), or a field programmable gate array(FPGA), or similar device. In one embodiment, the processing device 710comprises an IC device including a free-standing composite CNT structure(e.g., packaged IC device 301 having thermal interface devices 300 a,300 b, or packaged IC device 601 having thermal interface devices 600 a,600 b). However, it should be understood that the disclosed thermalinterface devices comprising a composite CNT structure may find use inother types of IC devices (e.g., memory devices).

[0044] Computer system 700 also includes system memory 720 coupled withbus 705, the system memory 720 comprising, for example, any suitabletype of random access memory (e.g., dynamic random access memory, orDRAM). During operation of computer system 700 an operating system 724,as well as other programs 728, may be resident in the system memory 720.Computer system 700 may further include a read-only memory (ROM) 730coupled with the bus 705. During operation, the ROM 730 may storetemporary instructions and variables for processing device 710, and ROM730 may also have resident thereon a system BIOS (Basic Input/OutputSystem). The computer system 700 may also include a storage device 740coupled with the bus 705. The storage device 740 comprises any suitablenon-volatile memory—such as, for example, a hard disk drive—and theoperating system 724 and other programs 728 may be stored in the storagedevice 740. Further, a device 750 for accessing removable storage media(e.g., a floppy disk drive or CD ROM drive) may be coupled with bus 705.

[0045] The computer system 700 may include one or more input devices 760coupled with the bus 705. Common input devices 760 include keyboards,pointing devices such as a mouse, and scanners or other data entrydevices. One or more output devices 770 may also be coupled with the bus705. Common output devices 770 include video monitors, printing devices,and audio output devices (e.g., a sound card and speakers). Computersystem 700 further comprises a network interface 780 coupled with bus705. The network interface 780 comprises any suitable hardware,software, or combination of hardware and software capable of couplingthe computer system 700 with a network (or networks) 790.

[0046] It should be understood that the computer system 700 illustratedin FIG. 7 is intended to represent an exemplary embodiment of such acomputer system and, further, that this computer system may include manyadditional components, which have been omitted for clarity and ease ofunderstanding. By way of example, the computer system 700 may include aDMA (direct memory access) controller, a chip set associated with theprocessing device 710, additional memory (e.g., a cache memory), as wellas additional signal lines and buses. Also, it should be understood thatthe computer system 700 may not include all of the components shown inFIG. 7.

[0047] Embodiments of a methods 200, 500 for fabricating compositecarbon nanotube structures 300, 600—as well as embodiments of a thermalinterface device comprising such a composite CNT structure—having beenherein described, those of ordinary skill in the art will appreciate theadvantages of the disclosed embodiments. The disclosed composite CNTstructures provides high thermal conductivity, high mechanical strength,and good chemical stability. Further, these composite CNT structures maybe fabricated to a very thin and uniform thickness. Also, the disclosedcomposite CNT structures may be fabricated using well known, low costmethods (e.g., CVD, PECVD, electroplating, electroless plating,sputtering, etc.), and their fabrication and use as thermal interfacedevices is compatible with existing assembly and process conditions.

[0048] The foregoing detailed description and accompanying drawings areonly illustrative and not restrictive. They have been provided primarilyfor a clear and comprehensive understanding of the disclosed embodimentsand no unnecessary limitations are to be understood therefrom. Numerousadditions, deletions, and modifications to the embodiments describedherein, as well as alternative arrangements, may be devised by thoseskilled in the art without departing from the spirit of the disclosedembodiments and the scope of the appended claims.

What is claimed is:
 1. A method comprising: forming a sacrificial layeron a substrate; forming a metal layer on the sacrificial layer;anodizing the metal layer to form a layer of a porous metal oxide; andforming carbon nanotubes in pores of the porous metal oxide layer. 2.The method of claim 1, further comprising removing excess metal oxidematerial from the pores of the porous metal oxide layer prior to formingthe carbon nanotubes.
 3. The method of claim 2, wherein the pores extendthrough the porous metal oxide layer into the sacrificial layer.
 4. Themethod of claim 1, further comprising depositing a catalyst in the poresof the porous metal oxide layer prior to forming the carbon nanotubes.5. The method of claim 5, wherein the catalyst comprises iron, nickel,cobalt, rhodium, platinum, or yttrium.
 6. The method of claim 1, furthercomprising separating the porous metal oxide layer and carbon nanotubesfrom the sacrificial layer and the substrate to form a free-standingcomposite carbon nanotube (CNT) structure.
 7. The method of claim 6,wherein separating the porous metal oxide layer and carbon nanotubesfrom the sacrificial layer and substrate comprises dissolving thesacrificial layer.
 8. The method of claim 7, wherein the sacrificiallayer is dissolved in a solution including an acid.
 9. The method ofclaim 8, wherein the acid comprises phosphoric acid, succinic acid, orsulfuric acid.
 10. The method of claim 8, wherein the sacrificial layeris dissolved under application of an anodic potential.
 11. The method ofclaim 6, further comprising attaching the composite CNT structure to acomponent.
 12. The method of claim 11, wherein the component comprises asemiconductor wafer, an integrated circuit die, a heat spreader, or aheat sink.
 13. The method of claim 11, wherein attaching the compositeCNT structure to the component comprises attaching the composite CNTstructure to the component using a low melting point metal alloy. 14.The method of claim 13, wherein the low melting point metal alloycomprises a solder.
 15. The method of claim 11, wherein attaching thecomposite CNT structure to the component comprises compressing thecomposite CNT structure against the component.
 16. The method of claim15, wherein the composite CNT structure is compressed against thecomponent under a pressure in a range up to approximately 10 Kg/cm². 17.The method of claim 6, wherein the composite CNT structure has athickness in a range of approximately 2 μm to 20 μm.
 18. The method ofclaim 1, wherein the carbon nanotubes are formed to a height extendingabove an upper surface of the porous metal oxide layer.
 19. The methodof claim 1, wherein the carbon nanotubes are formed by chemical vapordeposition (CVD) or plasma enhanced CVD.
 20. The method of claim 1,wherein the metal layer comprises aluminum and the porous metal oxidelayer comprises aluminum oxide.
 21. The method of claim 1, wherein thesacrificial layer comprises vanadium, titanium, or tungsten.
 22. Themethod of claim 1, wherein the metal layer is anodized under a positivevoltage and in the presence of a solution including an acid.
 23. Themethod of claim 22, wherein the acid comprises one of phosphoric acid,succinic acid, sulfuric acid, and oxalic acid.
 24. The method of claim22, wherein the positive voltage comprises a voltage in a range ofapproximately 1 to 60 volts.
 25. A device comprising: a porous metaloxide layer; and a number of carbon nanotubes disposed in pores of theporous metal oxide layer.
 26. The device of claim 25, wherein the metaloxide layer comprises aluminum oxide.
 27. The device of claim 25,wherein at least some of the carbon nanotubes extend above a surface ofthe porous metal oxide layer.
 28. A device comprising: an integratedcircuit die; and a thermal interface device coupled with a surface ofthe die, the thermal interface device comprising a layer of a porousmetal oxide and a number of carbon nanotubes disposed in pores of theporous metal oxide layer.
 29. The device of claim 28, further comprisinga heat spreader coupled with the thermal interface device.
 30. Thedevice of claim 29, further comprising: a second thermal interfacedevice coupled with the heat spreader, the second thermal interfacedevice comprising a layer of a porous metal oxide and a number of carbonnanotubes disposed in pores of the porous metal oxide layer; and a heatsink coupled with the second thermal interface device.
 31. A systemcomprising: a bus; and a device coupled with the bus, the deviceincluding an integrated circuit die, and a thermal interface devicecoupled with a surface of the die, the thermal interface devicecomprising a layer of a porous metal oxide and a number of carbonnanotubes disposed in pores of the porous metal oxide layer.
 32. Thesystem of claim 31, wherein the device further includes a heat spreadercoupled with the thermal interface device.
 33. The system of claim 32,wherein the device further includes: a second thermal interface devicecoupled with the heat spreader, the second thermal interface devicecomprising a layer of a porous metal oxide and a number of carbonnanotubes disposed in pores of the porous metal oxide layer; and a heatsink coupled with the second thermal interface device.
 34. The system ofclaim 31, wherein the device comprises a processing device.
 35. Thesystem of claim 34, further comprising a memory coupled with the bus.36. A method comprising: forming a sacrificial layer on a substrate;forming a layer of a porous material on the sacrificial layer; andforming carbon nanotubes in pores of the layer of porous material. 37.The method of claim 36, further comprising depositing a catalyst in thepores of the layer of porous material prior to forming the carbonnanotubes.
 38. The method of claim 36, further comprising dissolving thesacrificial layer to separate the layer of porous material and carbonnanotubes from the sacrificial layer and the substrate.
 39. A methodcomprising: disposing a substrate in a plating bath including a platingsolution, the plating solution including ions of a metal and carbonnanotubes; and forming a layer of the metal on the substrate, the metallayer including a number of the carbon nanotubes.
 40. The method ofclaim 39, wherein the metal comprises one of tin, indium, copper,nickel, cobalt, iron, cadmium, chromium, ruthenium, rhodium, rhenium,antimony, bismuth, platinum, gold, silver, zinc, palladium, andmanganese.
 41. The method of claim 39, wherein the carbon nanotubescomprise up to approximately 20 percent by weight of the platingsolution.
 42. The method of claim 39, wherein the metal layer is formedby electroplating.
 43. The method of claim 42, wherein the platingsolution further comprises a complexing agent.
 44. The method of claim42, wherein the plating solution further comprises an additive toregulate a property of the metal layer.
 45. The method of claim 44,wherein the additive comprises polyethylene glycol or a di-sulfide. 46.The method of claim 42, further comprising depositing a seed layer onthe substrate prior to forming the metal layer.
 47. The method of claim39, wherein the metal layer is formed by electroless plating.
 48. Themethod of claim 47, wherein the plating solution further comprises acomplexing agent and a reducing agent.
 49. The method of claim 48,wherein the reducing agent comprises one of formaldehyde, hypophosphite,dimethyl amine borane, and hydrazine hydrate.
 50. The method of claim47, wherein the plating solution further comprises a substance to adjusta pH of the plating solution.
 51. The method of claim 47, wherein theplating solution further comprises an additive to regulate a property ofthe metal layer.
 52. The method of claim 51, wherein the additivecomprises one of polyethylene glycol and a di-sulfide.
 53. The method ofclaim 47, further comprising depositing a catalyst on the substrateprior to forming the metal layer.
 54. The method of claim 47, furthercomprising heating the plating solution in the plating bath.
 55. Themethod of claim 39, further comprising applying an electric field acrossthe metal layer to align the carbon nanotubes in the metal layer. 56.The method of claim 55, wherein the carbon nanotubes are alignedsubstantially perpendicular to a surface of the substrate.
 57. Themethod of claim 39, wherein the substrate comprises a semiconductorwafer, an integrated circuit die, a heat spreader, or a heat sink. 58.The method of claim 39, further comprising separating the metal layerincluding the carbon nanotubes from the substrate to form afree-standing composite carbon nanotube (CNT) structure.
 59. The methodof claim 58, further comprising attaching the composite CNT structure toa component.
 60. The method of claim 59, wherein the component comprisesa semiconductor wafer, an integrated circuit die, a heat spreader, or aheat sink.
 61. The method of claim 59, wherein attaching the compositeCNT structure to the component comprises: depositing a layer of a lowmelting point metal alloy on a surface of the composite CNT structure;and attaching the composite CNT structure to the component using thelayer of low melting point metal alloy.
 62. The method of claim 61,wherein the low melting point metal alloy comprises a solder.
 63. Themethod of claim 58, wherein the composite CNT structure has a thicknessin a range of approximately 2 μm to 20 μm.
 64. A device comprising: asubstrate; and a layer of metal disposed over a surface of thesubstrate, the metal layer having a number of carbon nanotubes dispersedtherein.
 65. The device of claim 64, wherein each of the carbonnanotubes has a primary axis substantially aligned in a directionperpendicular to the surface of the substrate.
 66. The device of claim64, wherein the substrate comprises a semiconductor wafer, an integratedcircuit die, a heat spreader, or a heat sink.
 67. The device of claim64, wherein the substrate comprises a sacrificial substrate and thelayer of metal having the carbon nanotubes is separable from thesacrificial substrate.
 68. The device of claim 64, wherein the metalcomprises one of tin, indium, copper, nickel, cobalt, iron, cadmium,chromium, ruthenium, rhodium, rhenium, antimony, bismuth, platinum,gold, silver, zinc, palladium, and manganese.
 69. A device comprising:an integrated circuit die; and a thermal interface device coupled with asurface of the die, the thermal interface device comprising a metallayer having a number of carbon nanotubes dispersed therein.
 70. Thedevice of claim 69, further comprising a heat spreader coupled with thethermal interface device.
 71. The device of claim 70, furthercomprising: a second thermal interface device coupled with the heatspreader, the second thermal interface device comprising a metal layerhaving a number of carbon nanotubes dispersed therein; and a heat sinkcoupled with the second thermal interface device.
 72. A systemcomprising: a bus; and a device coupled with the bus, the deviceincluding an integrated circuit die, and a thermal interface devicecoupled with a surface of the die, the thermal interface devicecomprising a metal layer having a number of carbon nanotubes dispersedtherein.
 73. The system of claim 72, wherein the device further includesa heat spreader coupled with the thermal interface device.
 74. Thesystem of claim 73, wherein the device further includes: a secondthermal interface device coupled with the heat spreader, the secondthermal interface device comprising a metal layer having a number ofcarbon nanotubes dispersed therein; and a heat sink coupled with thesecond thermal interface device.
 75. The system of claim 72, wherein thedevice comprises a processing device.
 76. The system of claim 75,further comprising a memory coupled with the bus.